Pen



FIG. 1 is a bottom front perspective view of a pen showing my new design;

FIG. 2 is a side elevation view of the pen of FIG. 1;

FIG. 3 is a bottom plan view of the pen of FIG. 1; and,

FIG. 4 is a top plan view of the pen of FIG. 1. 

The ornamental design for a pen, as shown and described. 